Loudspeakers have been constructed for some time utilizing rigid, light-weight diaphragms constructed of foamed plastics such as polystyrene. The combination of light weight and rigidity provides efficient tonally accurate sound reproduction. Exemplary structures are disclosed in U.S. Pat. Nos. 2,905,260; 3,046,362; 3,351,719; 3,509,290; 3,553,392; and 3,651,283. The use of rigid light weight expanded plastic diaphragms has permitted the use of broad surface diaphragms as in U.S. Pat. Nos. 3,351,719 and 3,509,290, which, acting as a piston, require only one-third the diaphragm excursion of the ordinary conical diaphragms.
Until now rigid, broad surface diaphragms have been driven using the same driving configuration as utilized with the conventional conical paper diaphragm. Using conventional magnet assemblies, the driver diameter is typically limited to one-half to two inches. When only one such driver is utilized it is centrally positioned and as the diaphragm area is increased the acoustic efficiency and the accuracy of sound reproduction decrease.